Fine particle liquid filtration media

ABSTRACT

The present invention provides a filter media comprising (a) a nonwoven composite material comprising a stabilized mixture of thermoplastic microfibers and at least about 50%, by weight, of a secondary fibrous material such as pulp or polymeric staple fibers; (b) a first outer nonwoven web comprising a substantially uniform nonwoven web of autogenously bonded multicomponent fibers; and (c) a second outer nonwoven web wherein the nonwoven composite material is positioned between the first outer nonwoven web and second outer nonwoven web. The filter material is well suited to filtering liquid borne particulate matter ranging in size from 5μ to about 25μ.

This application claims priority from U.S. Provisional Application No.60/098,526 filed on Aug. 31, 1998.

FIELD OF THE INVENTION

The present invention relates to nonwoven composite fabrics suitable foruse for fine particle liquid filtration.

BACKGROUND OF THE INVENTION

Nonwoven fabrics have been used for a variety of filtration andfiltration-like applications. As an example, fine fiber webs such asmeltblown fabrics and laminates thereof have commonly been used withinair filtration media. Meltblown fabrics comprise a web of randomlyinter-laid fine fibers, which provide a structure having excellentbarrier properties. Generally, as the average fiber diameter decreasesthere is a corresponding decrease in the average pore size of thefabric. Thus, fabrics with finer fibers or smaller diameter fiberstypically have increased barrier properties when compared to like websof relatively larger fiber size. Therefore, due to fine fibersachievable in meltblown fiber webs and the excellent barrier propertiesresulting therefrom, meltblown fiber webs have been used in a variety ofair filtration media such as, for example, in HEPA filters as discussedin U.S. Pat. No. 4,824,451, bag filters as discussed in U.S. Pat. No.5,586,997, and filtering bacteria from fluids as discussed in U.S. Pat.No. 5,582,907 to Paul.

However, the needs of air filtration media often vary considerably fromthose of liquid filtration media. Notably, the particle sizedistribution within a liquid stream is typically much larger thanparticles associated with an air stream. In this regard, air filtrationmedia are often expected to collect particles having a size less thanabout 5μ whereas with fine particle liquid filtration the particle sizeoften varies between about 5μto about 30μ. Multilayer filtration mediasuitable for air filtration, such as that described above, will oftenhave an unacceptably short filter life when used for liquid filtration.While having an excellent filtration efficiency, the particles sizesassociated with liquid filtration are typically of a size anddistribution that the meltblown webs and/or laminates thereof quicklybecome fully saturated and/or create high pressure drops.

Additionally, meltblown fiber nonwoven webs can be relatively weakfabrics and often cannot, by themselves, withstand the conditionsexperienced by liquid filtration media. Thus, meltblown webs have beensupported in multilayer structures to provide filter media orfilter-like articles with improved strength and/or durability. In thisregard, meltblown fiber nonwoven webs have been laminated with spunbondfiber nonwoven webs in order to provide a material with a combination ofgood strength and barrier properties. As examples thereof,spunbond/meltblown/spunbond media have been used in sterilization wrapsand other like media such as, for example, those described in U.S. Pat.No. 5,464,688 to Timmons et al. and U.S. Pat. No. 4,041,203 to Brock etal. However, many nonwoven laminates are point bonded to form anintegrated structure and, in this regard, the point bonds undesirablyincrease pressure drop without a corresponding increase in filter lifeand/or efficiency. Additional spunbond fabrics and/or laminates thereofutilized in filtration media are described in PCT Publication Nos. WO96/13319 and WO 95/13856. Further, composite meltblown nonwoven fabrics,such as those described in U.S. Pat. No. 4,100,324 to Anderson et al.,have also been used in liquid filtration applications wherein thecomposite nonwoven fabric is supported by a spunbond carrier sheet and afelt material.

However, there exists a need for filtration media suitable for use inliquid filtration that has good filtration efficiency and yet which alsoexhibit a suitable or even extended filtration life. Further, thereexists a need for such materials which can provide the desiredfiltration efficiency and filter life and which are capable of servicinghigh volumes without creating high pressure drops. Still further, thereexists a need for such materials that can be economically produced andwhich can withstand the pressures, handling and other conditionscommonly associated with liquid filtration.

SUMMARY OF THE INVENTION

The aforesaid needs are fulfilled and the problems experienced by thoseskilled in the art overcome by the filtration media of the presentinvention comprising (a) a nonwoven composite material having a firstand second side and comprising a matrix of thermoplastic microfibershaving within said matrix at least about 50%, by weight, of a secondarymaterial; (b) a first nonwoven web proximate the first side of thenonwoven composite material and comprising a substantially uniformnonwoven web of bonded fibers; and (c) a second nonwoven web proximatethe second side of the nonwoven composite material such that thenonwoven composite material is positioned between the first and secondnonwoven web. Desirably the nonwoven composite material and the firstand second nonwoven webs form an integrated, autogenously bondedlaminate. The nonwoven composite material desirably has a basis weightbetween about 30 g/m² and about 300 g/m² and further the secondarymaterial of the nonwoven composite material desirably comprises afibrous material such as, for example, pulp or polymeric staple fibers.The substantially uniform nonwoven material desirably comprises anonwoven web having inter-fiber bonds throughout the web such as, forexample, an autogenously bonded web of crimpedpolyethylene/polypropylene bicomponent fibers having a density betweenabout 0.01 g/cm³ and about 0.2 g/cm³.

In a further aspect of the invention, liquids containing particulatematter can be filtered by providing the filter media of the presentinvention, supporting the filter media on a foraminous surface, and thendrawing the liquid through the filter media, wherein particulate matteris collected in the filter media as the liquid passes therethrough. Theliquid to be filtered desirably contains a substantial amount ofparticulate matter having a particle size of from about 5μ to about 25μ.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially elevated side view of a three layer material ofthe present invention shown partially broken away;

FIG. 2 is a side cross-sectional view of a three-layer material of thepresent invention;

FIG. 3 is a partially elevated side view of a four layer filter materialof the present invention shown partially broken away;

FIG. 4 is a schematic illustration of a method of making the nonwovencomposite fabrics of the present invention; and

FIG. 5 is a schematic illustration of a process of filtering liquidscontaining particulate matter.

DEFINITIONS

As used herein and in the claims, the term “comprising” is inclusive oropen-ended and does not exclude additional unrecited elements,compositional components, or method steps.

As used herein the term “nonwoven fabric” or “nonwoven web” means a webhaving a structure of individual fibers or threads which are interlaid,but not in an identifiable manner as in a knitted fabric. Nonwovenfabrics or webs have been formed from many processes such as forexample, meltblowing processes, spunbonding processes, air-laid andbonded-carded web processes.

As used herein the term “microfibers” or “fine fibers” means smalldiameter fibers having an average fiber size not greater than about 20microns. As used herein “fiber size” refers to the diameter of roundfibers or the mean diameter for non-round fibers.

As used herein the term “spunbonded fibers” or “spunbond fibers” refersto small diameter fibers of drawn or substantially oriented polymer.Generally, spunbond fibers are formed by extruding molten thermoplasticmaterial as filaments from a plurality of fine, usually circularcapillaries of a spinneret with the diameter of the extruded filamentsthen being rapidly reduced such as, for example, in U.S. Pat. No.4,340,563 to Appel et al., U.S. Pat. No. 3,802,817 to Matsuki et al.,U.S. Pat. No. 3,542,615 to Dobo et al. and U.S. Pat. No. 5,382,400 toPike et al.; the entire contents of each of the aforesaid references areincorporated herein by reference. Spunbond fibers are generally nottacky when they are deposited onto a collecting surface and thus oftenrequire additional mechanical or chemical bonding to form an integratedstabilized web.

As used herein the term “meltblown fibers” means fibers which aregenerally formed by extruding a molten thermoplastic material through aplurality of fine, usually circular, die capillaries as molten threadsor filaments into converging high velocity, usually hot, gas (e.g. air)streams which attenuate the filaments of molten thermoplastic materialto reduce their diameter, which may be to microfiber diameter.Thereafter, the meltblown fibers are generally carried by the highvelocity gas stream and are deposited on a collecting surface to form aweb of randomly dispersed meltblown fibers. Such a process is disclosed,for example, in Naval Research Laboratory Report No. 4364, “Manufactureof Super-fine Organic Fibers” by V. A. Wendt, E. L. Boon, and C. D.Fluharty, Naval Research Laboratory Report No. 5265, “An Improved Devicefor the Formation of Super-fine Thermoplastic Fibers” by K. D. Lawrence,R. T. Lukas, and J. A. Young, U.S. Pat. No. 3,849,241 to Butin et al.;U.S. Pat. No. 3,849,241 to Butin et al. and U.S. Pat. No. 5,213,881 toTimmons et al.; the entire contents of the aforesaid references areincorporated herein by reference. Meltblown fibers are often microfiberswhich can be continuous or discontinuous and are generally tacky whendeposited onto a collecting surface.

As used herein the term “polymer” generally includes but is not limitedto, homopolymers, copolymers, such as for example, block, graft, randomand alternating copolymers, terpolymers, etc. and blends and/ormodifications thereof. Furthermore, unless otherwise specificallylimited, the term “polymer” shall include all possible spatialconfigurations of the molecule. These configurations include, but arenot limited to, isotactic, syndiotactic and/or random symmetries.

As used herein the term “monocomponent” fiber refers to a fiber formed asingle, continuous polymer segment.

As used herein the term “multiconstituent fibers” refers to fibers thathave been formed from at least two polymers extruded from the sameextruder. Multiconstituent fibers do not have the various polymercomponents arranged in constantly positioned distinct zones across thecross-sectional area of the fiber and the various polymers are usuallynot continuous along the entire length of the fiber, instead usuallyforming fibrils or protofibrils which start and end at random.Biconstituent fibers are a specific class of multiconstituent fiberswherein the fiber comprises two distinct polymers.

As used herein the term “blend” means a mixture of two or more polymerswhile the term “alloy” means a sub-class of blends wherein thecomponents are immiscible but have been compatibilized.

As used herein, “ultrasonic bonding” means a process performed, forexample, by passing the fabric between a sonic horn and anvil roll asillustrated in U.S. Pat. 4,374,888 to Bornslaeger.

As used herein “point bonding” means bonding one or more layers offabric at numerous small, discrete bond points. For example, thermalpoint bonding generally involves passing one or more layers to be bondedbetween heated rolls such as, for example an engraved patterned roll anda flat calender roll. The engraved roll is patterned in some way so thatthe entire fabric is not bonded over its entire surface, and the anvilroll is usually flat. As a result, various patterns for engraved rollshave been developed for functional as well as aesthetic reasons. Oneexample of a pattern has points and is the Hansen Pennings or “H&P”pattern with about a 30% bond area and with about 200 bonds/square inchas taught in U.S. Pat. No. 3,855,046 to Hansen et al.

As used herein, the term “autogenous bonding” refers to bonding betweendiscrete parts and/or surfaces independently of external mechanicalfasteners or external additives such as adhesives, solders, and soforth. As an example, multicomponent fibers and multiconstituent fiberscan be autogenously bonded by developing inter-fiber bonds at fibercontact points without destroying the fiber structure.

DESCRIPTION OF THE INVENTION

In reference to FIGS. 1 and 2, multilayer filtration media 10 cancomprise a nonwoven composite material 12, a first substantially uniformnonwoven fabric 14 and a second nonwoven fabric 16 such that nonwovencomposite material 12 is disposed there between. The first substantiallyuniform nonwoven fabric 14 desirably comprises a low density and/orhigh-loft material and faces upstream of the composite material 12 suchthat larger particles are collected within first substantially uniformnonwoven fabric 14 prior to reaching nonwoven composite material 12.

Nonwoven composite materials suitable for use with the present inventioninclude materials comprising a mixture or stabilized matrix ofthermoplastic fibers and a distinct secondary particulate or fibrousmaterial therein. As an example, suitable nonwoven composite materialsmay be made by a process in which at least one meltblown die head isarranged near a chute through which other materials are added to the webwhile it is forming. Suitable secondary materials include, but are notlimited to, pulp, cellulose, feathers, polymeric staple fibers and/orother fibrous or particulate matter. Desirably, the composite materialcomprises a matrix of thermoplastic fibers and a secondnon-thermoplastic material. Composite materials made from such a processare often referred to as “coform” materials and examples of suchprocesses are described in commonly assigned U.S. Pat. No. 4,818,464 toLau, U.S. Pat. No. 4,100,324 to Anderson et al., and U.S. Pat. No.5,350,624 to Georger et al., and U.S. patent application Ser. No.08/882,308 to Strack et al. filed Jun. 25, 1997; the entire contents ofthe aforesaid patents and application are incorporated herein byreference. The composite material desirably comprises fine fibers havingan average fiber diameter of less than about 20μ and even more desirablybetween about 0.5μ and about 15μ and still more desirably between about1μ and about 10μ. Additionally, the fine fiber composite materialdesirably has a basis weight between about 30 g/m² to about 300 g/m² andeven more desirably between about 50 g/m² to about 150 g/m².

The secondary material desirably comprises between about 50% by weightand about 85% by weight and still more desirably between about 70% byweight and about 80% by weight of the nonwoven composite material. Theuse of the secondary material within the fine fiber matrix creates amaterial having a fiber structure which is considerably more irregularand non-uniform as compared to microfiber meltblown fabrics morecommonly utilized in filtration applications. Further, due to the moreirregular internal structure of the composite material, relative tomicrofiber meltblown nonwoven webs, larger average pore structures arecreated. However, the composite material has a structure with lessuniform fiber orientation and as a result has numerous tortuous pathsthrough the fabric. This forces particles traveling through thecomposite material to flow in a multitude of directions which allows thefilter to trap particles smaller than that of the complex pathway. As aspecific example, the fine fiber nonwoven composite material cancomprise a nonwoven web of polypropylene meltblown fibers and thesecondary material can comprise generally ribbon-shaped pulp fibershaving an average length between about 30μ and 50μ with an averageheight of about 5μ. Desirably, the nonwoven composite material has amean pore size ranging from about 15μ to about 45μ and, still moredesirably, a mean pore size of about 30μ. In a further aspect, thenonwoven composite material desirably has a wide range of pore sizessuch as, for example, having pore sizes ranging from about 10μ to about140μ. Despite having a mean flow pore size larger than many of theparticles to be trapped, the complex and tortuous pathways through thecomposite material provide a filtration medium capable of efficientlyentraping particles of a size from about 5μ to about 25μ. Moreover, sucha structure also provides filtration media having good pressure drop aswell as capacity and filter life.

The filtration media also has a first or upstream layer comprising asubstantially uniform nonwoven web of continuous, bonded fibers. Thefirst nonwoven web desirably has inter-fiber bonds throughout the weband an average pore size greater than that of the composite material. Asused herein the term “substantially uniform” means a material which doesnot have regions of significantly high and low densities such as pointbonded fabrics or other similar fabrics having high density and lowdensity regions across the face or central portion of the fabric. Havingrelatively high-density areas, such as those created at bond points,generally decreases the filtration efficiency of the first nonwoven weband also increases the pressure drop across the filtration media. Thesubstantially uniform, bonded nonwoven fabric can have inter-fiber bondscreated by an external adhesive applied to the fibers or autogenousinter-fiber bonding. Desirably, the outer nonwoven web is directlyattached to the composite material. However, other intermediatematerials may be disposed therebetween.

An exemplary substantially uniform nonwoven material comprisesautogenously bonded fibers and still more desirably comprisesautogenously bonded multicomponent spunbond fibers. As used herein theterm “multicomponent fibers” refers to fibers which have been formedfrom at least two polymers extruded from separate extruders but spuntogether to form one fiber. Bicomponent fibers refer to a common,specific class of multicomponent fiber wherein the fiber comprises twodistinct components. The polymers are arranged in substantiallyconstantly positioned distinct zones or segments across thecross-section of the fibers and extend continuously along the length ofthe fibers. The configuration of such fibers may be, for example, asheath/core arrangement wherein one polymer is surrounded by another ormay be a side-by-side arrangement, a pie arrangement or otherarrangement. Multicomponent fibers are taught in U.S. Pat. No. 5,108,820to Kaneko et al., U.S. Pat. No. 4,795,668 to Krueger et al., U.S. Pat.No. 5,336,552 to Strack et al. and in U.S. Pat. No. 5,382,400 to Pike etal.; the entire content of each of the aforesaid patents is incorporatedherein by reference. For bicomponent fibers, the polymers are desirablypresent in ratios of 75/25, 50/50, 25/75 or any other desired ratios.The fibers may also have various shapes such as, for example, ribbon,hollow, multilobal and so forth. Desirably the autogenously bondednonwoven web has a basis weight of at least 15 g/m² and desirablybetween about 30 g/m² to about 300 g/m² and even more desirably a basisweight between about 50 g/m² to about 150 g/m². Multiconstituent fiberscapable of forming interfiber bonds are also believed suitable for usewith the present invention. In a preferred embodiment, the autogenouslybonded nonwoven web can comprise a multicomponent spunbond fiber websuch as is described in U.S. Pat. No. 5,382,400 to Pike et al., U.S.Pat. No. 5,534,339 to Stokes and U.S. Pat. No. 5,855,784 to Pike et al.;the entire contents of the aforesaid patents are incorporated herein byreference. As a specific example, the autogenously bonded nonwoven webcan comprise a high-loft web comprising crimpedpolyethylene/polypropylene conjugate fibers having a density betweenabout 0.01 g/cm³ and about 0.2 g/cm³. As a further example, crimpedpolyethylene/nylon spunbond fiber webs are also believed well suited foruse in the present invention.

Desirably, the substantially uniform nonwoven webs are autogenouslybonded using hot air such as developed by “through-air bonding.” As usedherein, through-air bonding refers to a process of bonding nonwovenfiber webs in which hot air, that is sufficiently hot to melt one of thepolymers comprising the fibers, is forced through the web. The hot airmelts the lower melting polymer component and the resolidification ofthe melted polymer forms bonds between the filaments at contact pointsto integrate the web. As an example, an exemplary through-air bondingprocess suitable for use with the fabrics of the present invention canemploy an air velocity between 100 and 500 feet per minute and dwelltimes up to about 6 seconds. Exemplary through-air bonding equipment candirect hot air, having a temperature above the melting temperature ofone component and below the melting temperature of another component,from a surrounding hood, through the web, and into a perforated rollersupporting the web. Alternatively, the through-air bonder may be a flatarrangement wherein the air is directed vertically downward onto theweb. It will be appreciated by those skilled in the art that therequisite air temperature, air velocity and dwell time will vary withrespect to the particular polymers comprising the nonwoven web, thecomposition or structure of the same as well as the degree of bondingdesired.

The multilayer filtration media further comprises a second or downstreamnonwoven web positioned such that the nonwoven composite web is disposedbetween the first and second nonwoven webs. Desirably, the secondnonwoven layer comprises a material capable of providing additionalfiltration properties, strength and/or support to the nonwoven compositeweb. The second nonwoven web can comprise one or more of the materialsdiscussed herein above with regard to the first outer nonwoven web. Inone aspect of the invention, the second nonwoven web can comprisespunbond fibers comprising monocomponent, multiconstituent ormulticomponent fibers. Desirably, the second nonwoven web likewisecomprises a substantially uniform material. The particular polymer(s) orpolymer blends used in the second nonwoven web can be selected toachieve the desired strength, abrasion resistance and/or other desiredcharacteristics. The second or downstream nonwoven web desirably has abasis weight between about 15 g/m² and about 225 g/m² and still moredesirably has a basis weight between about 30 g/m² and about 100 g/m².In one embodiment of the present invention, both the first and secondnonwoven webs can comprise through-air bonded high-loft, multicomponentspunbond fiber webs. Further, it is desirable that the second nonwovenweb likewise comprise a polymer having a softening and/or melting pointwhich is the same as or substantially similar to the low meltingcomponent of the upstream or first nonwoven web so as to allowautogenous bonding of the entire laminate without the need forexternally applied adhesive, point bonding and/or other additional meansof attachment. However, where additional integrity is desired themultiple layers can be bonded as desired by one or more means known inthe art such as use of an adhesive, mechanical crimping or stitching,thermal bonding, and/or ultrasonic bonding. The potential negativeimpact of adhesives or point bonding on filtration properties may belimited and/or eliminated by bonding only the edges of the multilayerfiltration material.

In a further aspect of the present invention, the upstream side of thefilter media can comprise a plurality of substantially uniform andautogenously bonded layers. In reference to FIG. 3, the multilayerfilter media 20 can comprise a nonwoven composite material 22 havingfirst side 24 and second side 26. First autogenously bonded nonwoven web30 can be attached to first side 24 of nonwoven composite material 22.Second autogenously bonded nonwoven web 28 can be attached to the secondside 26 of nonwoven composite material 22. Third autogenously bondednonwoven web 32 can be attached to the first autogenously bondednonwoven web 30 thereby forming a four-layer laminate. Desirably, thefirst and third nonwoven webs 30 and 32 comprise fibers having at leastone polymer having the same or substantially similar melting points.Still more desirably, the first and third autogenously bonded nonwovenwebs 30 and 32 comprise the same materials. The first and third nonwovenwebs 30 and 32 can have the same or different basis weights. Further,the first and third autogenously bonded nonwoven webs can comprisematerials having the same or different pore structures. Desirably, thenonwoven fabric having a larger average pore size is preferablypositioned upstream of the lower loft, lower density structure therebyallowing the layers to act as a depth filter and provide a filter mediumhaving improved filter life and/or capacity. As a particular example,the first nonwoven web can comprise crimped polyethylene/polypropylenebicomponent spunbond fiber web having a density in the range betweenabout 0.01 and 0.2 g/cm³ and the third nonwoven web can comprise acrimped polyethylene/polypropylene bicomponent spunbond fiber web havinga lower density than the first web. In one embodiment, the third layercan have a lower density by comprising a nonwoven web of spunbond fiberswith a higher degree of crimp than that of the first nonwoven web.

In reference to FIG. 4, a process line 50 for fabricating a laminate ofthe present invention is disclosed. Hoppers 52 a and 52 b may be filledwith the respective polymeric components 53 a and 53 b. The polymericcomponents are then melted and extruded by the respective extruders 54 aand 54 b through polymer conduits 56 a and 56 b and through spinneret58. Spinnerets are well known to those skilled in the art and,generally, include a housing containing a spin pack which includes aplurality of plates stacked one on top of the another with a pattern ofopenings arranged to create the desired flow paths through thespinneret. As the extruded filaments extend below spinneret 58, a streamof air from quench blower 60 quenches bicomponent filaments 62. Thefilaments 62 are drawn into a fiber draw unit or aspirator 64 and thenonto traveling foraminous surface 66, with the aid of vacuum 68, to forman unbonded layer of bicomponent spunbond fibers 70. The unbondedbicomponent fiber layer 70 may be lightly compressed by compression orcompaction rollers 72. The bicomponent fiber layer can optionally bethrough-air bonded prior to formation of the composite nonwovenmaterial. Those skilled in the art will appreciate that a bondedspunbond fiber web could be made previously and wound on a supply rolland fed into the present process.

Fine fiber composite material 101 can be made using the desired processequipment such as coform apparatus 80. Polymer is progressively heatedto a molten state as it advances through extruder 82 and intomeltblowing dies 84 and 85. Meltblowing dies 84 and 85 can be configuredso that two streams of attenuating gas per die converge to form a singlestream of gas which entrains and attenuates molten threads 88, as thethreads 88 exit small holes or orifices 86 of the meltblowing dies 84and 85. The molten threads 88 are attenuated into fibers and desirably,depending upon the degree of attenuation, microfibers. Thus, eachmeltblowing die 84 and 85 has a corresponding single stream of gas (notshown) containing entrained and attenuated polymer fibers. The gasstreams containing polymer fibers are aligned to converge at animpingement zone 90.

One or more types of secondary fibers 92 and/or particulates are addedto the two streams of thermoplastic polymer fibers or microfibers at theimpingement zone 90. Introduction of the secondary fibers 92 into thetwo streams of thermoplastic polymer fibers 88 is designed to produce agraduated distribution of secondary fibers 92 within the combinedstreams of thermoplastic polymer fibers. This may be accomplished bymerging a secondary gas stream containing the secondary fibers 92between the two streams of thermoplastic polymer fibers 88 so that allthree gas streams converge in a controlled manner.

Apparatus for accomplishing this merger may include a conventionalpicker roll assembly 96 which has a plurality of teeth that are adaptedto separate a mat or batt 98 of secondary fibers into the individualsecondary fibers 92. The mat or batt 98 of secondary fibers which is fedto the picker roll 96 may be a sheet of pulp fibers (if a two-componentmixture of thermoplastic polymer fibers and secondary pulp fibers isdesired), a mat of staple fibers (if a two-component mixture ofthermoplastic polymer fibers and a secondary staple fibers is desired)or both a sheet of pulp fibers and a mat of staple fibers (if athree-component mixture of thermoplastic polymer fibers, secondarystaple fibers and secondary pulp fibers is desired). FIG. 4 furtherillustrates that the secondary gas stream 94 carrying the secondaryfibers 92 is directed between the streams of thermoplastic polymerfibers 88 so that the streams contact at the impingement zone 90. Due tothe fact that the thermoplastic polymer fibers 88 are usually stillsemi-molten and tacky at the time of incorporation of the secondaryfibers 92 into the thermoplastic polymer fiber streams, the secondaryfibers 92 are usually not only mechanically entangled within the matrixformed by the thermoplastic polymer fibers 88 but are also thermallybonded or joined to the thermoplastic polymer fibers 88. The mergedstream 100 of thermoplastic polymer fibers and secondary fibers arecollected to form a coherent matrix of fibers, which is nonwovencomposite web 101, on the surface of the spunbond fibers 70. Vacuumboxes (not shown) can assist in retention and/or formation of the matrixon the surface of the spunbond fibers. Alternately, a collecting devicecan be located in the path of the composite stream and the nonwovencomposite web fed onto the multicomponent spunbond fiber material.

A second nonwoven web 104, such as an autogenously bonded bicomponentspunbond fiber web, can be unwound from a supply roll 102 and fed overthe nonwoven composite web 101. The three layers can then, while in aface-to-face relation, be fed through through-air bonder 108 therebybonding the respective layers to form an integrated, autogenously bondedthree layer laminate 110. The laminate 110 can be wound on winder roll112 or further processed and/or converted in-line as desired.

The method set forth above, for making a laminate of the presentinvention, can be modified in one or more ways as desired. As anexample, the entire laminate can be made in-line, replacing the unwind102 with a second spunbond forming apparatus. Additionally, to achievethe desired basis weights or web characteristics it may likewise bedesirable to employ a series of spunbond or coform forming apparatus.Still further, each of the individual layers can be made off-line andunwound in series, and bonded together to form the filter media.However, typically the coform material lacks sufficient integrity to bewound/unwound without the use of a carrier sheet such as, for example, alightweight spunbond sheet. Carrier sheets often have basis weightsbetween about 10 g/m² and 16 g/m². Further, adhesive can be applied toone or more of the materials in order to increase the peel strength ofthe multilayer laminate. Still further, additional materials can beadded to the multilayer laminate in order to further improve thestrength, abrasion resistance or other properties of the multilayerlaminate as desired.

The filtration media of the present invention can have a variety ofuses. The filter media can be converted as desired for use with asupport member or within a filter element such as, for example, filtercartridges, frames, wire mesh, screen supports and so forth. As specificexamples thereof the fabric can be used in filtration systems associatedwith metal working, auto grinding, aluminum rolling, sewage or wastewater treatment and so forth. In reference to FIG. 5, filtration media152 can be unwound from supply roll 150 and travels in the direction ofthe arrow associated therewith. Container 154 holds contaminated liquid156 having particulate matter therein. Contaminated liquid 156 is drawnthrough filtration media 152 thereby producing filtered liquid 158 thatis collected in second container 160. The liquid flows through thefilter media in the direction of the arrows associated therewith.Filtration media 152 can be supported on an open or foraminous surface159 such as, for example, a mesh screen, a series of pinner bars, oranother substantially open structure. As filtration media 152 filtersparticulate matter within contaminated liquid 156 the filter mediaeventually becomes saturated forming spent filter medium 153. The spentfiltration medium 153 can be fed to a waste disposal apparatus 162and/or recycling apparatus. The filtration media 152 is desirably cycledthrough the filtration system such that filter medium is at leastsubstantially saturated at or fully saturated at or near the end of thefiltering window. In this regard, contaminated liquid 156 can be drawnthrough filter medium 152 with the aid of a vacuum (not shown) and, asthe filtration medium becomes more highly saturated, the pressure dropacross the fabric increases. When a particular pressure drop is reachedthe filtration medium can be cycled through the filtration zone orwindow. Additionally and/or alternatively, the filtration medium cansimply be cycled through the filtration window at a predetermined rate,e.g. at a constant rate or at set intervals. Desirably, the filtrationmedia has a filtration efficiency of at least 50% for particles rangingin size from about 5μ to about 25μ.

EXAMPLE 1

A 51 g/m² nonwoven web of crimped bicomponent spunbond fibers is formedin accord with U.S. Pat. No. 5,382,400 to Pike et al. The bicomponentspunbond fibers comprise 50/50 components of polypropylene (ExxonChemical Co. polypropylene 3155) and polyethylene (Dow Chemical Co.polyethylene 6811) having a side-by-side configuration. The bicomponentspunbond fiber webs are through-air bonded to form an autogenouslybonded nonwoven web having inter-fiber bonds dispersed throughout theweb. The autogenously bonded bicomponent spunbond fiber web is then slitto the desired width and wound onto a winder roll. The autogenouslybonded spunbond fiber web is subsequently unwound from the winder rolland fed onto a foraminous surface. A coform material is formed directlyupon the surface of the autogenously bonded spunbond fiber web forming atwo-layer spunbond/coform material which is then wound on a winder roll.The 90 g/m² coform material is made in accord with U.S. Pat. No.4,100,324 to Anderson et al. The meltblown fibers comprise polypropylene(Montell North America polypropylene PF015) and the secondary fiberscomprise a fluff pulp (Georgia Pacific fluff pulp RM 4821) with thefluff pulp comprising about 60%, by weight, of the coform. The two-layerspunbond/coform material is subsequently unwound from the winder rolland fed onto a foraminous surface. Bicomponent spunbond fibers, the sameas those described above with regard to the 51 g/m² spunbond fiber web,are formed directly upon the coform layer of the spunbond/coformmaterial. The three layers are then passed through a through-air bonderthereby forming a cohesive three-layer laminate.

While various patents and other reference materials have beenincorporated herein by reference, to the extent there is anyinconsistency between incorporated material and that of the writtenspecification, the written specification shall control. In addition,while the invention has been described in detail with respect tospecific embodiments thereof, it will be apparent to those skilled inthe art that various alterations, modifications and other changes may bemade to the invention without departing from the spirit and scope of thepresent invention. It is therefore intended that the appended claimscover all such modifications, alterations and other changes.

What is claimed is:
 1. Filtration media consisting essentially of: anonwoven composite material having a first and second side andcomprising a stabilized matrix of thermoplastic microfibers havingwithin said microfiber matrix at least about 50%, by weight, of asecondary material; a first nonwoven web adjacent said first side ofsaid nonwoven composite material wherein said first nonwoven webcomprises a substantially uniform nowoven web having inter-fiber bondsthroughout the web; and a second nonwoven web adjacent said second sideof said nonwoven composite material and wherein said first and secondnonwoven webs and said nonwoven composite material comprise anintegrated autogenously bonded multilayer laminate.
 2. The filtrationmedia of claim 1 wherein said nonwoven composite material has a basisweight between about 30 g/m² and about 300 g/m².
 3. The filtration mediaof claim 2 wherein said secondary material of the nonwoven compositematerial comprises a fibrous material selected from pulp, polymericstaple fibers, and feathers.
 4. The filtration media of claim 2 whereinsaid secondary material of the nonwoven composite material comprises afibrous, non-polymeric material.
 5. The filtration media of claim 4wherein said secondary material of the nonwoven composite materialcomprises pulp.
 6. The filtration media of claim 3 wherein said firstnonwoven web comprises a nonwoven web of continuous fibers selected fromthe group consisting of multicomponent and multiconstituent fibers. 7.The filtration media of claim 6 wherein said first nonwoven webcomprises an autogenously bonded web of crimped multicomponent spunbondfibers having a density between about 0.01 g/cm³ and about 0.2 g/cm³. 8.The filtration media of claim 7 wherein said first nonwoven web ofmulticomponent spunbond fibers comprises a web ofpolyethylene/polypropylene bicomponent spunbond fibers.
 9. Thefiltration media of claim 8 wherein said second nonwoven web comprises anonwoven web of continuous fibers selected from the group consisting ofmulticomponent and multiconstituent fibers.
 10. The filtration media ofclaim 8 wherein said composite material comprises meltblown fibershaving an average fiber size less than about 15μ.
 11. The filtrationmedia of claim 9 wherein said second nonwoven web comprises asubstantially uniform, autogenously bonded nonwoven web of crimpedmulticomponent spunbond fibers and further wherein said fibers of saidsecond nonwoven web comprise polyethylene and a second polymer.
 12. Thefiltration media of claim 11 wherein said first autogenously bondednonwoven web has a basis weight between about 30 g/m² and 150 g/m², andsaid second nonwoven web has a basis weight of between about 30 g/m² and150 g/m².
 13. The filtration media of claim 7 further comprising a thirdnonwoven web wherein said third nonwoven web comprises a substantiallyuniform and autogenously bonded nonwoven web of crimped multicomponentspunbond fibers and further wherein said third nonwoven web has adensity greater than the density of said first nonwoven web.
 14. Thefiltration media of claim 13 wherein said nonwoven composite materialhas a basis weight between about 50 g/m² and 300 g/m², said first andthird nonwoven webs have a combined basis weight between about 50 g/m²and 150 g/m², and said second nonwoven web a basis weight of betweenabout 30 g/m² and 150 g/m².